A commonly encountered problem is the need to remediate soils that have been contaminated with industrial chemicals such as oily wastes. Soils are often contaminated with hydrocarbons such as oil and fuels. In some instances the contaminants may include materials such as asbestos.
Various thermal treatments for remediating contaminated land have been proposed. For example, U.S. Pat. No. 5,769,569 describes an in-situ thermal desorption system that is used to mobilize and remove non-volatile and semi-volatile hydrocarbons from contaminated soil. Combustion is initiated in a burner underneath the contaminated soil zone and persistent hydrocarbons are thermally desorbed by direct heating of the contaminated zone. The generated soil vapors are collected and the desorbed vapors are processed in a hydrocarbon recovery and treatment assembly.
German patent application 2 020 612, filed on 28 Apr. 1970, describes a method and device for eliminating oil that has penetrated into the soil. A borehole is drilled in the earth down to the contaminated region. The oil in the soil is brought to a combustion temperature. Once the oil has reached its combustion temperature and is burning automatically, then it is only necessary to supply oxygen to sustain the combustion. The oil is thus incinerated within the earth at its location, i.e. in-situ treatment.
A similar process is described in German application DE 36 19 494 A1, filed on 6 Oct. 1986. Injection torches are introduced into the soil to generate a high temperature, using added air at the deepest point of the injection hole. This heats the ground sufficiently such that combustible substances such as waste oils and the like are ignited, thus achieving in-situ incineration of the soil contamination. There may be combustion of the contaminated soil up to the surface.
A further such process is described in the International application WO 2007/066125, filed on 8 Dec. 2006. Land contaminated with combustible materials may be cleaned or remediated by combusting the materials in-situ (i.e. within the ground). Combustion of the material may be self-sustaining in that it may only be necessary to supply sufficient energy to ignite the material. Once ignited, combustion may proceed in the presence of oxygen. This is contrasted with known thermal remediation processes which require continuous energy input to sustain the incineration.
There is an ongoing need for cost-effective methods of treating contaminated material.